Monitoring EMG activity has been infrequently used to promote a relaxed state before taking measurements (25). A tape measure has frequently been used to measure the distances, but some investigators have opted for unmarked sections of strings initially, so as to remove any measurer bias. Calipers have also been used (25) and may provide a more accurate linear distance because they do not need to conform to the contours of the body, as does a measuring tape or string.
The validity of determining scapular position has usually been assessed by comparison with radiographic measurements. Although assumed to be the “gold” standard, there are limitations with this method (13) and this is reflected in the reliability of repeated measurements taken from radiographs not always being high (6). The validity of the skin surface palpation technique using cadaver shoulders has been assessed by comparison with the actual location revealed by dissection, but there are limitations in inferring results from cadaver to living subjects (13). Data comparing direct measurements from cadaver shoulders with radiographic measurements are lacking. The method used to determine scapular position should ideally demonstrate high reliability (intraclass correlation coefficient [ICC] > 0.9) and validity (r > 0.9). Acceptable reliability and validity may be considered as >0.8 (21). As can been seen from Table 1, a range of reliability and validity values have been reported for the various techniques.
It has been assumed that the strength of the scapular abductor and retractor muscles may influence the position of the scapula, if the scapular abductors are strong and the retractors are relatively weak, this may promote excessive scapular abduction at rest. There has been one study (4) that investigated the relationship between scapular position at rest and the strength of middle trapezius and pectoralis minor muscles for 30 male and 30 female healthy subjects, mean age 26 years. Isometric peak force generated from a maximal contraction lasting 4 to 5 seconds was measured with a stabilized handheld dynamometer. It was positioned against the lateral aspect of the scapula for the middle trapezius test and against the anterior aspect of the shoulder for the pectoralis minor test. The normalized position of the scapula was determined as described in Table 1 for DiVeta et al. (4). It was found that there was no significant relationship between scapular position and middle trapezius force (r = 0.20), pectoralis minor force (r = 0.14), and ratio of muscle forces (r = 0.01). This study had a number of limitations. The intratester reliability of determining the normalized scapular position (ICC = 0.78) along with its validity (ICC = 0.73-0.79) reported in another study (6) was not high. The muscle strength tests were found to have high intratester reliability (ICC = 0.96), but their validity has not been established (15). The use of healthy subjects probably limited the range of scapular abduction position values and likelihood of detecting a relationship. The inclusion of subjects with excessive scapular abduction would have been desirable.
The relative muscle length of the scapula abductors or retractors has been postulated to influence scapular position; short abductor or long retractor muscles may position the scapula in excessive abduction. To examine this possible link, the length of pectoralis minor muscle was measured in 50 healthy male and female subjects with a mean age of 27 years (2). Using palpation and a computerized electromagnetic measurement system, the distance between the coracoid process to the fourth rib adjacent to the sternum was used as the length of pectoralis minor at rest. This procedure was validated against cadaver measurements (ICC = 0.96), but reliability was not reported. Pectoralis muscle length was normalized by dividing by the subject's height, and subjects were then divided into 2 groups: the short pectoralis minor group with a length less than the mean minus 1 SD and the long pectoralis minor group with a length greater than the mean plus 1 SD.
Scapular position was determined by palpation and using a tape measure to determine 2 distances. The first was measured anteriorly between the sternal notch and coracoid process, and the second was measured posteriorly between the acromion and thoracic spine. The anterior measure was divided by the posterior measure to generate a scapula index. The reliability and validity of this value and its components were not established. The results revealed significant but low correlations between pectoralis minor length and sternal notch to coracoid process distance (r = 0.48) and scapula index (r = 0.37). There was no significant correlation (r = 0.17) between muscle length and distance between the acromion and thoracic spine. It is surprising that a significant relationship was found for the anterior measure but not the posterior, considering that the length of pectoralis minor would supposedly influence the position of the scapular landmarks.
There have been studies examining the influence of stretching the scapular abductors or strengthening scapular retractors or a combination on the position of the scapula at rest (Table 2). All studies used subjects with some degree of forward shoulder posture. The study by Wang et al. (29) found no change in scapular position after 6 weeks of home-based strengthening and stretching exercises. The duration of the static stretches was 10 seconds. Roddey et al. (22) found that a 2-week stretching program of 30-second duration significantly reduced the resting scapular abduction position in subjects with moderate forward head/rounded shoulder posture. Kluemper et al. (12) used a 6-week supervised strengthening and stretching program and revealed that the intervention group significantly reduced forward shoulder posture. It seems that a supervised program may be more effective than a home-based one and that a stretch duration of 30 seconds is preferable to 10 seconds. There is also an indication that stretching the scapular abductors may be more important than strengthening the scapular retractors. Although changes in the position of the scapula were reported, there are notable weaknesses in the study designs. The techniques used to determine the position of the scapula displayed high reliability, but their validity is questionable, either not reported or r < 0.8. None of the studies measured strength or flexibility pre or post intervention, so it is unclear how effective the intervention was in influencing these parameters and the actual mechanism behind the change.
The question arises as to which properties of the muscle are most likely to influence scapular position. Bearing in mind the limitations of some of the research, the finding that muscle strength was not related to scapular position (4) may not be all that surprising because there is only low-level muscular activity about the scapula at rest. It is assumed that increased strength would lead to increased muscle tension at rest. It could be argued that a measure of muscular endurance is more likely to be related to scapular position than muscular strength, but then again, muscular strength might be reflective of muscular endurance. It needs to be noted that muscle tension on its own would not influence position unless there was a concurrent change in the resting length of the muscle. A significant relationship was reported (2) between pectoralis minor muscle length and scapular position. Forward shoulder posture was associated with shorter pectoralis minor length. Once again, the finding is not surprising because it is hard to envisage an abducted scapulae posture without short pectoralis minor length, and this on its own does not necessitate cause and effect. An individual with relatively short clavicles would present with an abducted scapulae posture, and the resting length of pectoralis minor would be short but not the cause of the posture. Short muscle length is more readily to be an influential factor if associated with greater musculotendinous stiffness. It could be more likely that a short stiff muscle would influence postural alignment. Resting muscle length, muscle range of motion, or EMG activity at rest does not necessarily provide an accurate measure of muscle stiffness at rest. There are active and passive elements that can contribute to musculoskeletal stiffness (14). Further investigation is required to determine any link between muscle stiffness and postural alignment.
Findings from the prospective intervention studies have shown that stretching the anterior chest muscles on its own (22) or in combination with strengthening exercises for the scapular retractors (12) can alter the position of the scapula at rest in individuals with abducted scapulae. Although these results are encouraging, more work is required in this area to address some of the limitations of these studies. Future research should employ reliable and valid methods to determine scapular position and pre- and post-intervention measures of muscular strength, endurance, resting length, and stiffness. To help determine which component of the intervention is most effective and if the results are additive, the intervention groups should include stretching only, strengthening only, and stretching and strengthening. The training sessions should be of progressive intensity and preferably supervised or a training diary kept of the subjects' adherence to the program and their perceived rate of exertion so as to monitor compliance and effort. A follow-up some period after completion of the intervention would also provide valuable information as to the permanency of any changes.
Although there are some data showing that stretching exercises may alter the position of the scapula at rest, the studies have limitations and further quality research is needed. The practical implication is that restraint should be practiced when considering the promotion of strengthening exercises for the correction of abnormal scapular posture until further evidence becomes available.
No source of funding was used to assist in the preparation of this review. The author has no conflicts of interest that are directly relevant to the contents of this review.
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